1. Field of the Invention
This invention relates to diaphragms for use in pumps and valves, and more particularly to a diaphragm including a solid polytetrafluoroethylene layer adhered to a thermoplastic elastomeric layer.
2. Background Information
Diaphragm pumps are used in pumping a wide variety of materials especially when the materials are abrasive, have high viscosity, or consist of slurries that might damage other pump designs. These pumps are often air driven which is advantageous in pumping flammable liquids or in environments where electrically driven equipment could otherwise be hazardous. However, electrically or otherwise mechanically driven designs also find wide utility. Due to the wide nature of different materials these pumps are used to move, a correspondingly wide variety of materials are used in their construction. These include plastics and metals. For the same reason the critical driving member, i.e., the pump diaphragm, typically must be manufactured in a variety of materials.
Chemically resistant layers, such as those made of polytetrafluoroethylene (PTFE), are widely used in industry to protect sensitive parts of machinery or equipment from the corrosive effects of acids or other chemicals. One such use is in two piece pump diaphragms commonly used with air or electrically driven diaphragm pumps. In the two piece diaphragms, an outer PTFE overlay diaphragm is commonly used to protect an inner rubber diaphragm from materials that would cause rapid failure of the rubber part alone. In some other cases, the PTFE provides the sole material of construction of the diaphragm.
Such two piece diaphragms commonly utilize a PTFE layer and a thermoset material such as neoprene. While the PTFE layer tends to protect the diaphragm from corrosive effects of some materials, the thermoset rubber material is subject to failure due to other factors such as exposure to relatively low temperatures, tearing and abrasion. Moreover, conventional thermosetting elastomers may be relatively difficult and/or expensive to process, and provide inferior performance relative to thermoplastic elastomers or thermoplastic rubbers.
However, thermoplastic elastomers or rubbers tend to be difficult to bond to PTFE, and tend to delaminate when subjected to repeated flexure, such as experienced in pump diaphragm applications.
Thus, a need exists for a composite diaphragm and a method for making such a diaphragm, that utilizes a layer of PTFE bonded to a thermoplastic elastomer.